This invention relates generally to wireless networks, and, more specifically, to setting up a group call in a wireless network.
Wireless networks (also called cellular networks) are built around the premise of a one-to-one call; that is, each channel in the wireless network is used by only one mobile station at a time. There are some applications, however, where a one-to-many call is useful. In a public safety application, for example, a dispatcher may want to communicate to a number of mobile stations simultaneously. While a one-to-many call is technically feasible in today""s wireless network, the current call setup scheme may be too slow for public safety and other time-intensive applications.
In current call setup, a mobile switching center receives a call for a mobile station and queries a home location register for that mobile station""s current location. The home location register reports the local area (a group of contiguous cells in the wireless network) in which the mobile station last registered. Since the mobile switching center knows only the approximate location of the mobile station, it causes all of the base stations in the local area to transmit a paging message on a paging channel to determine the exact location of the mobile station. When a mobile station receives the page, it responds to the nearest base station. The base station notifies the mobile switching center, which routes the call to the base station to be delivered to the mobile station.
While the above-described call setup is relatively efficient for a one-to-one call, repeating all of the steps for each member of a group may take considerable time and be very cumbersome. Paging for and locating all of the group members individually may cause heavy message traffic and require many system resources.
According to one aspect of this invention, a method is provided for use in a wireless network for setting up a call among a group of mobile stations in the wireless network. The wireless network has a plurality of cells, each cell includes a base station that has a plurality of channels for communicating with mobile stations located within the cell. The method includes the steps of each base station allocating a channel as a group call channel, each mobile station in the group acknowledging allocation of the group call channel, and each base station that did not receive an acknowledgement within a time period freeing the group call channel.
According to a further aspect of this invention, the wireless network has a plurality of local areas, each local area comprising a plurality of adjacent cells and each mobile station registering with the wireless network when it changes local areas. The step of allocating a channel includes each base station in the local area with a registered group member allocating a channel for the group call. According to another aspect of the invention, each base station that receives an acknowledgement from one of the mobile stations in the group sends a presence acknowledgment to each mobile station in the base station""s cell.
In accordance with a further aspect of this invention, each channel may be a plurality of timeslots on a radio frequency, and the step of sending an acknowledgement may be each mobile station generating a random number and sending the acknowledgement to the base station on a timeslot selected by the random number. Further, each mobile station may repeatedly send the acknowledgement to the base station until receipt of the base station""s presence acknowledgement. In accordance with yet another aspect of this invention, each mobile station may send an identification of itself to the base station with the acknowledgement, said wireless network determining whether one or more of the group members are present on the group call.
According to another aspect of this invention, the wireless network has a plurality of local areas in which each mobile station registers when it is in any cell in the local area. The method further includes the step wherein each base station in the local area with a registered group member allocates a channel for the group call. Further, each base station that receives an acknowledgement from a mobile station sends a presence acknowledgement back to the mobile station.
In accordance with another aspect of the invention, a wireless network capable of setting up a group call includes a mobile switching center and a plurality of base stations connected to the mobile switching center. The mobile switching center is adapted to notify the plurality of base stations of a group call and the plurality of base stations are adapted to allocate a communication channel for the group call. Further, each of the plurality of base stations is adapted to deallocate the communication channel if it did not receive an acknowledgement within a predetermined time.
In accordance with another aspect of this invention, the wireless network includes a group location register that is adapted to store the location where the mobile stations in the group are currently located. Further, the base stations are organized into a plurality of local areas wherein the group location registers stores the local area where the mobile stations in the group are currently located. In accordance with a further aspect of the invention, the wireless network includes a group location register adapted to store a plurality of cells where group members may be located. Finally, the wireless network may be organized into a plurality of local areas and the group location registers storing the local areas where group members may be located.